/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.sql.connector.expressions.filter;

import java.io.Serializable;

import org.apache.spark.annotation.Evolving;
import org.apache.spark.sql.connector.expressions.Expression;
import org.apache.spark.sql.connector.expressions.NamedReference;

/**
 * Filter base class
 *
 * @since 3.3.0
 */
@Evolving
public abstract class Filter implements Expression, Serializable {

  protected static final NamedReference[] EMPTY_REFERENCE = new NamedReference[0];

  /**
   * Returns list of columns that are referenced by this filter.
   */
  public abstract NamedReference[] references();

  @Override
  public String describe() { return this.toString(); }
}
